Abstract: The double taxation of corporate income should discourage firms from incorporating. We investigate the extent to which the aggregate allocation of assets and taxable income in the U.S. between corporate and non-corporate firms responds to the size of this tax distortion during the period 1959-86. In theory, profitable firms should shift out of the corporate sector when the tax distortion is large, and conversely for firms with tax losses. Our empirical results provide strong support for all of these forecasts and imply that the resulting excess burden equals 16% of business tax revenue.